Aligned dipolar Bose-Einstein condensate in a double-well potential: From cigar shaped to pancake shaped

Abstract

We consider a Bose-Einstein condensate (BEC), which is characterized by long-range and anisotropic dipole-dipole interactions and vanishing s-wave scattering length, in a double-well potential. The properties of this system are investigated as functions of the height of the barrier that splits the harmonic trap into two halves, the number of particles (or dipole-dipole strength) and the aspect ratio λ, which is defined as the ratio between the axial and longitudinal trapping frequencies ωz and ωρ. The phase diagram is determined by analyzing the stationary mean-field solutions. Three distinct regions are found: a region where the energetically lowest lying stationary solution is symmetric, a region where the energetically lowest lying stationary solution is located asymmetrically in one of the wells, and a region where the system is mechanically unstable. For sufficiently large aspect ratio λ and sufficiently high barrier height, the system consists of two connected quasi-two-dimensional sheets with density profiles whose maxima are located either at ρ = 0 or away from ρ = 0. The stability of the stationary solutions is investigated by analyzing the Bogoliubov de Gennes excitation spectrum and the dynamical response to small perturbations. These studies reveal unique oscillation frequencies and distinct collapse mechanisms. The results derived within the mean-field framework are complemented by an analysis based on a two-mode model.

Dipolar condensates confined in a toroidal trap: Ground state and vortices

“…[19], the magnetization direction is used to induce SB, while in Ref. [20] it is the number of dipoles in the double well that drives it. The mechanism triggering the effect is the presence of a repulsive barrier in systems that are dominated by attractive interactions.…”

“…Optical lattices have been already addressed in the literature (see the review [2] and references therein), as well as double-well potentials [19,20], but the present work is to our knowledge the first where dipolar condensates are studied in toroidal traps. Experimentally, toroidal traps can be realized by shining the condensate with a blue-detuned laser beam [21].…”

Modification of roton instability due to the presence of a second dipolar Bose-Einstein condensate

“…Describing the condensate by a single mean-field wavefunction, the existence of an instability island immersed in an otherwise stable region has been predicted to exist for certain parameter combinations [16]. Furthermore, macroscopic quantum self-trapping, a phenomenon intensely studied for s-wave interacting BECs [17][18][19], has been predicted to occur for a dipolar BEC in a cigar-shaped double-well potential [14,15] and in a toroidal trap [20]. The transition from the macroscopic quantum self-trapping to the Josephson oscillation regime has been interpreted using a single twomode model that treats the left well and the right well as being occupied by macroscopic wavefunctions 1 and 2 , respectively.…”

Dipolar Bose–Einstein condensates in triple-well potentials

“…Dipolar BECs in double-well potentials have been investigated in [11,12]. In this system three major phases have been found: In the first both wells are populated equally.…”

“…The second is the symmetry-broken phase (macroscopic quantum self-trapping, MQST), in which the majority of the particles populates one well, and the third is the unstable phase, where the condensate wave function collapses. It has been pointed out in [12] and [13] that MQST is a dynamical effect arising from the interaction of the particles which reflects itself in the nonlinearity of the GPE.…”